1. Background of the Invention
The present invention relates to a guide bar, to a chain comprising such a bar, and to an engine equipped with such a chain.
2. Brief Description of the Related Art
A drive chain may be used for the transmission of a movement and, in particular, for the synchronization of the elements constituting a timing system in an internal combustion engine of an automobile vehicle.
It is known from EP-A-1 072 816 to provide, in a drive chain guide bar, a recess which extends from an outer edge of the bar in the direction of the opposite edge, between orifices for passage of pins for articulation of this bar with other, so-called inner bars, used for constituting the links of the chain.
The known outer, or guide bar of EP-1 072 816 functions correctly, but is relatively heavy, which has a negative influence on its inertia and on the dynamic behaviour of a chain comprising a large number of such bars. In addition, the tools for manufacturing such an outer bar must be produced by a plurality of machining operations, involving the corresponding manipulations. This results in risks of error during the machining and control operations.
It is a more particular object of the present invention to overcome these drawbacks by proposing a guide bar for a drive chain of the afore-mentioned type, whose sequence of manufacture may be optimalized, while it presents excellent mechanical properties and an inertia compatible with relatively great accelerations, for example at the level of a sprocket of a timing system in an engine.
To that end, the invention relates to a guide bar for a drive chain, this bar being provided with two orifices for passage of a pintle pin, each orifice being substantially triangular in shape, with substantially identical edges, in the form of an arc of circle and concave, this bar being provided with a recess which extends from an outer edge of the bar, in the direction of an opposite edge, between these orifices. This bar is characterized in that it comprises, on either side of the afore-mentioned recess, two series of two convex edges in the form of arc of circle, each of these convex edges being centred on the geometrical centre of a concave edge of a triangular orifice for passage of a pintle pin.
Thanks to the invention, the same geometrical centre is used for defining one of the concave edges of an orifice for passage of a pintle pin and one of the convex edges of the bar in the vicinity of this orifice, which makes it possible to produce tools for cutting out these edges by machining, without having to displace the blank of the tool during manufacture. In the same way, the operations of dimensional control of these tools and of these edges may be effected by taking the same point of reference.
According to advantageous but non-obligatory aspects of the invention, this bar incorporates one or more of the following characteristics:
The bar forms, between one of its convex edges and the concave edge of the adjacent orifice centred on the same geometrical centre, a band in the form of a section of ring, centred on the same geometrical axis and of substantially constant width. This band makes it possible effectively to withstand the mechanical stresses undergone by the bar, particularly when the pintle pin is fitted and then shrunk in the orifice of substantially triangular section.
Depending on the case, the common geometrical centre may be located in the vicinity of the outer edge of the bar or between the triangular orifice and a median axis of the bar, located half-way between the two triangular-section orifices.
The radii of curvature of the convex edges of the bar arranged on the same side of the recess are substantially equal.
A transition edge is provided, arranged between two convex edges formed on the same side of the recess, this transition edge likewise being circular and convex and having a smaller radius of curvature than the respective radii of curvature of the two convex edges between which it is arranged.
A transition edge is provided, arranged between one of the convex edges of the bar and the edge of the afore-mentioned recess, this transition edge likewise being circular and convex and having a smaller radius of curvature than that of the afore-mentioned convex edge.
The afore-mentioned transition edge is tangential to the edges between which it is arranged. In addition, the radius of curvature of the transition edges may be provided to have a value equal to e+0.365 mm, where e is the thickness of the bar.
The invention also relates to a chain which comprises at least one outer, or guiding, bar as described hereinabove. Such a chain may be used under severe conditions, while it is relatively easy to manufacture, with satisfactory tolerances, and the mechanical stresses due to the shrinking of the pins fitted in the triangular-section orifices are distributed substantially uniformly in the material constituting these outer bars.
Finally, the invention relates to an engine, particularly an internal combustion engine, equipped with a chain as described hereinabove. Such an engine functions under optimalized conditions of transmission of the efforts of traction of the chain.